Today, the most common practice of recording and transferring information is through the use of plain paper. One of the most widely recognized methods of recording information on plain paper is through the use of a photocopier. A photocopier scans an image, possibly performs some processing on the image and then reproduces the scanned image onto a piece of plain paper.
Until recently, prior art copiers mainly operated using analog signals. In other words, the operations of scanning the image, processing the image and then reproducing the image were all performed in analog. More recently, many functions of the copier have been performed in the digital arena. However, in either the analog or digital case, the function of the photocopier remains the reproduction of an original image onto a piece of plain paper.
The change from analog-to-digital signals in photocopiers allows several new operations to be performed. One new operation that may be performed is the encryption of information. Encryption is a technique whereby data may be stored in a format such that the data cannot be deciphered easily. In other words, encryption provides a mechanism for encoding data. There are numerous techniques in the prior art for encryption. However, all of these prior art techniques require that the data be digital. In the prior art, some copiers have been able to rearrange the information on the page in an attempt to provide encryption. One problem with providing encryption through simply rearranging the data on the page is that it isn't very secure. It would be advantageous to use a photocopier to perform encryption of digital data into plain paper such that it is secure.
In the prior art, some limited methods for storing digital information on plain paper have been set forth. One example of digital information being stored on paper is the use of bar codes. Bar codes are single dimension digital data in which typically ten digits of information are placed on a paper horizontally to store information. By scanning the bar codes in a relatively horizontal direction, the information encoded into the bar codes may be read. These scans usually occur very quickly. Note that the greater the height of the bar code (in the vertical direction), the less horizontal the scan is required to be to obtain the information. Also note that because bar codes are horizontal, there is an inherent limit to the number of bar codes which may be used to store digital information on a piece of paper. For more information on bar codes, see "Information Encoding with Two-Dimensional Bar Codes," authored by T. Pavlidis, J. Swartz and Y. Wang, COMPUTER, June 1992. See also U.S. Pat. No. 5,113,445 disclosing the placement of bar codes onto paper. It is desirable to store more digital information on a piece of plain paper than by using bar codes.
The present invention provides a method and apparatus for placing data on plain paper. In one embodiment, digital data is placed onto plain paper with a digital photocopier. The present invention also provides a method and apparatus for encrypting digital data such that the data remains secure upon reading the plain paper.